In recent years, due to an increasing interest in energy saving, there have been proposed many types of permanent magnet motors each of which uses a Nd.Fe.B rare-earth permanent magnet having a high residual flux density as a rotator, to thereby realize high efficiency.
In particular, as an electric motor for a compressor to be used in refrigeration equipment or air-conditioning equipment, an interior permanent magnet motor having a permanent magnet embedded in a rotator core is often used. In the rotator core, a plurality of magnet accommodating holes for embedding a plurality of permanent magnets are formed. For those magnet accommodating holes, in order to suppress a short-circuit flux of the permanent magnet when the magnet is embedded, space portions called flux barriers are formed at both end portions of the magnet accommodating hole in a longitudinal direction thereof. Moreover, for the magnet inserting holes, position determination projecting portions for determining an arrangement position of the magnet are formed. In the structure, the projecting portions are in surface-contact with the magnet at the both end portions of the magnet in a longitudinal direction thereof.
For example, a rotator of an interior permanent magnet motor disclosed in Patent Literature 1 includes a rotator core that has a plurality of hole portions for housing permanent magnets and is formed by laminating thin iron sheets with high magnetic permeability, and a plurality of permanent magnets housed and held in the hole portions, in which protrusions for punching are formed at both ends of the hole portions so that the rotator core and the permanent magnets are in surface-contact with each other, to thereby fix the permanent magnets.
A rotator of an interior permanent magnet motor disclosed in Patent Literature 2 includes a plurality of magnet inserting holes, permanent magnets inserted into the magnet inserting holes at approximately the center thereof, and demagnetization suppressing projecting portions. Each of the magnet inserting holes is formed along an outer peripheral edge of a rotator core. Between both end portions of the magnet inserting hole on the outer peripheral side and the outer peripheral edge of the rotator core, there are formed outer peripheral thin portions each having a predetermined radial dimension. In space in the both end portions of the magnet inserting hole into which the permanent magnet is not inserted, the demagnetization suppressing projecting portions are protruded from the outer peripheral side or the inner peripheral side of the magnet inserting hole at positions apart from the permanent magnet by a predetermined distance. Further, in the configuration, the shortest distance between the demagnetization suppressing projecting portion and the magnet inserting hole is smaller than a width of the magnet inserting hole in a radial direction thereof.
In a rotator of an interior permanent magnet motor disclosed in Patent Literature 3, in an outer diameter-side end portion of a magnet inserting hole on the inter-pole core portion side, a first magnet retaining portion protruding radially inward is formed, and in an outer diameter-side end portion of the magnet inserting hole on the inter-magnet inserting hole core portion side, a second magnet retaining portion protruding radially inward is formed.
Moreover, in some of the related-art electric motors, in order to operate an electric motor in a high temperature atmosphere of a compressor, much dysprosium (Dy) is added to increase J coercive force so that a rare-earth magnet is prevented from being demagnetized at high temperature. In particular, when an R32 coolant having a small global warming potential (GWP) is used, as compared to using a related-art 410A coolant, the temperature of the compressor is increased by 10° C. or more, and hence the addition amount of Dy is increased to increase the J coercive force.
For example, in a compressor disclosed in Patent Literature 4, a brushless DC motor and a compressor main body are concentrically arranged in a hermetically-sealed casing, a simple R32 coolant or an R32 rich mixed coolant is employed as a coolant to be taken, compressed, and discharged by the compressor main body, and J coercive force of a rare-earth magnet is set to 23 kOe or more.